The purpose of roof gutters is to collect rain-water and melted snow (in snow fall areas) that runs off a roof which is then discharged into connected downpipes to drainage or storage tanks. The latter purpose will become increasingly important in the future and it will become important that the water is relatively free of rotting organic matter.
Gutters have to be relatively simple and low in cost to manufacture and construct.
Most gutters are open and will collect leaves and debris from the roof and surrounding trees. These will be washed along in the gutter and can form a “dam” which will block the free flow of water in the gutter. Such blockages can cause the water to over-flow the back of the gutter and damage the eaves lining and ceilings. The leaves and debris will also contaminate the water that is discharged from the downpipes.
There have been many systems using mesh or a covering with holes that have been placed over the open face of gutters to prevent leaves and debris clogging the gutter and restricting or blocking the full flow of water. Some of these have additions to traditional gutters while others have been a complete assembly.
Gutters that have been covered with the finer mesh have the disadvantage that they do not readily allow the water to flow through into the gutter and can over-flow with heavier falls of rain. Gutters covered with the larger meshes allow the water to fall through the mesh to the gutter but also allow smaller leaves and debris to fall into the gutter and cause “damming” and blockage of the flow of water. Meshes also do not add to the strength of the gutter and gutter clips or straps are required to support the gutter which contribute to the collection of leaves and debris. Both fine and course meshes suffer the disadvantage of not providing wind uplift that occurs with a full surface to lift and blow the leaves out of the gutter.
With meshes made of metal wire, corrosion of the gutter and mesh can result if the metals from which the wire and the gutter are manufactured are dissimilar, causing bi-metallic corrosion due to an electro-chemical process.
Generally the flow of the rain-water off the roof is dispersed over the mesh surface and with lower intensity rainfalls does not cause a sufficient torrent of water to clear debris from the invert of the gutter and will allow this to accumulate to form dams when the velocity of the water is low. These in turn cause the velocity of water flow in the gutter from later flows to be reduced which will allow further debris to settle and collect at the “dams”. This continual process is likely to eventually block the gutter.